In a system for the development of aluminium lithographic printing plates of the type disclosed in EP-A-410500 (Agfa Gevaert NV), the apparatus comprises a housing with pairs of processing rollers rotatable on roller shafts supported within the housing. The processing rollers are positioned substantially parallel and in line contact with each other. Means are provided for feeding photographic sheet material between the rollers. The roller shafts are biased towards each other to exert a pressure on the photographic sheet material as it passes between the rollers. Such rollers can usefully be used as squeegee rollers at the exit of a chemical bath to remove excess chemicals from the sheet material as it exits the bath. A good removal of processing liquid is also required to reduce the drying time of the sheet material after the last process bath, and hence to reduce the energy use.
Aluminium lithographic printing plates produced in this manner are liable to suffer from the problem of bleeding. Briefly explained, bleeding is said to occur when shadows of silver are deposited beyond the trailing edge of an image part, generating a zone in which the density differs from the expected background density. The mechanism of bleeding is thought to include the fact that some silver in the image part is insufficiently strongly held to the base and is therefore somewhat mobile.
It is known that bleeding can be reduced by passing the sheet material between a pair of rollers under high pressure, in particular passing the sheet material between such rollers at the output end of a liquid processing station, the rollers being biased together with a force significantly greater than that required for them to act as efficient squeegee rollers. However the extra force required to reduce bleeding in this manner requires the use of larger diameter rollers and/or engineering arrangements that involve additional space and cost.